As is shown in FIG. 1, a conventional head drum assembly 100 for use in a video cassette recorder comprises a rotating shaft 1 divided into an upper and a lower parts, an upper head drum assembly 101 and a lower head drum assembly 102. The upper head drum assembly 101 includes an upper drum 2 with an inner part 2A and an outer side surface 2B, the outer side surface 2B being provided with a pair of head windows (not shown) having a predetermined width, a flange 3, a pair of heads 4, each of the heads having a head chip 4B adjoined to a head base 4A, and a rotor transformer 5. The inner part 2A of the upper drum 2 is provided with a top and a bottom surfaces 2A-1, 2A-2. The lower head drum assembly 102 includes a stator transformer 6, a lower drum 7 and two sets of bearings 8.
The upper drum 2 is joined with the upper part of the rotating shaft 1 via the flange 3; and the lower drum 7 is attached to the lower part of the rotating shaft 1 through the two sets of bearings 8.
The rotor transformer 5 may be attached at bottom of the flange 3 using, e.g., a bonding agent. The stator transformer 6 for producing a predetermined electric signal, on the other hand, may be fixed on the lower drum 7 using, e.g., a bonding agent, at a predetermined distance from the rotor transformer 5.
The upper drum 2 is provided with a first and a second pairs of tapped holes, each of the tapped holes from the first pair extending upward from the bottom surface 2A-2 of the inner part 2A thereof and each of the tapped holes from the second pair extending downward from the top surface 2A-1 of the inner part 2A thereof. Furthermore, each of the first pair of tapped holes has a first screw (S); and, likewise, each of the second pair of tapped holes has a second screw(S').
The heads 4 are secured to the bottom surface 2A-2 of the inner part 2A of the upper drum 2 by using the first screws (S) and the first pair of tapped holes in such a way that the head chips 4B from each of the heads 4 protrude past the outer side surface 2B of the upper drum 2 through the head windows. Vertical positions of the head chips 4B within the head drum assembly 100 are adjusted by using the second screws (S') in conjunction with the second pair of tapped holes.
In assembling the head drum assembly 100 shown in FIG. 1, each of the heads 4 is first fixed to the bottom surface 2A-2 of the inner part 2A of the upper drum 2 by using the first screw (S) and one of the first pair of tapped holes. Thereafter, the upper and the lower drums 2, 7 are assembled; and then the vertical positions of the head chips 4B within the head drum assembly 100 are adjusted using the second screws (S') and one of the second pair of tapped holes.
In such a head drum assembly, in order to securely fasten each of the heads 4 onto the bottom surface 2A-2 of the inner part 2A of the upper drum 2 and precisely adjust the vertical positions of the head chips 4B, each of the tapped holes from the first and the second pairs, and hence the screws, must be deep in length and wide in diameter.
However, the current trend in designing the upper drum is to make the inner part of the upper drum as thin as possible for the purpose of reducing the production cost thereof. When the inner part of the upper drum becomes too thin, however, tightening of the screws may cause a deformation of the inner part of the upper drum, making it difficult to securely fasten the heads to the bottom surface of the inner part of the upper drum and to precisely adjust the vertical positions of the head chips within the head drum assembly.